On Smallville, since Clark's dad has passed away and his mom has gone off to Washington D.C., he has no family left in town. In an effort to correct that situation, the producers of Smallville will be bringing his long lost cousin Kara (aka Supergirl) into the show for it's 7th season.
Her background will match that of the latest reboot of the character in DC comics: That she was also sent to earth from the doomed planet Krypton at the same time Clark was, but she was a teenager at the time. Through some glitch in her ship she has remained in suspended animation all this time on Earth.
According to executive producer Al Gough:
"But there was a problem, and she's been in suspended animation for the last 16 years. We'll find out in the season premiere that the big dam break in last season's finale is the reason she's finally awoken."
She will serve as a touchpoint to Clark's past, since she grew up on Krypton. She'll be able to tell him (and the viewers) all about what life was like there and about his parents. Also, unlike Clark who seems to have a fear of flying, she will be fully capable of doing so.
It looks like this final season is going to be much more "superhero-y" than previous seasons, what with Bizarro, Supergirl, Lex's super-army and no doubt more Justice League appearances. That sounds good to me, although the writers may find it progressively more difficult to keep any semblance of reality on the show as it veers further into comic book territory. On the other hand I think this is what the fans have been wanting more of for quite a while.
In regards to the Kara's ability to fly while Clark cannot, I'm curious to see how they handle that... Clark has had his entire life to get used to his powers, while Kara (as far as I know) will wake up in the season premiere and set foot on Earth for the first time. On krypton she didn't have super-powers, so I can't wait to see how the explain her getting a grip on suddenly having all these amazing abilities and mastering flight almost instantly while Clark continues to do his imitation of The Flash. :-)
Source: SciFi Wire